1. Field of the Invention
The present invention relates to a display device and a method for manufacturing the display device.
2. Description of the Related Art
In recent years, an active matrix display device is widely used, which displays an image or character information on an electronic appliance such as a monitor of a laptop personal computer or a desktop personal computer, a cellular phone, an audio reproducing device, a television set, a mobile terminal, a digital still camera, a video camera, or a viewer for viewing an image and a moving picture.
In the active matrix display device, active elements (for example, thin film transistors: TFTs) are arranged in matrix corresponding to pixels individually in a pixel portion which is to be a display region. As a switching element, the TFT controls voltage which is applied to the pixels, whereby desired images are displayed.
On an element substrate provided with an inverted staggered TFT of channel stopper type (also called channel protective type or etching stopper type) among TFTs used as switching elements, steps up to forming a pixel electrode are conducted using five photomasks (see Reference 1: Japanese Published Patent Application No. 2002-148658).
An example of a conventional inverted staggered TFT of channel stopper type and a conventional pixel portion including the inverted staggered TFT is shown in FIG. 6, FIG. 7, FIGS. 8A to 8C, and FIGS. 9A and 9B. FIG. 6 is a top view of one pixel and the periphery thereof, and FIG. 7 is a cross-sectional view along a line B-B′ of FIG. 6. FIGS. 8A to 8C and FIGS. 9A and 9B are cross-sectional views showing steps of manufacturing the pixel portion in a state of FIG. 7.
In one pixel, a TFT region 1141, a capacitor region 1142, and a wiring region 1143 are provided over a substrate 1101. In the TFT region 1141, a gate wiring 1102, a gate insulating film 1104, an i-type semiconductor layer 1113 having a channel formation region, a channel protective film 1108 formed of an insulating film, a source region 1118 and a drain region 1117 each formed of a semiconductor layer which has an impurity element imparting one conductivity type, a source wiring 1122, a drain electrode 1121, a protective film 1127, and a pixel electrode 1131 are provided.
In the capacitor region 1142, a capacitor wiring 1151, the gate insulating film 1104, the protective film 1127, and the pixel electrode 1131 are provided. Further, in the wiring region 1143, the source wiring 1122 is provided.
The capacitor region 1142 has a structure in which the capacitor wiring 1151 formed of the same material of the gate wiring 1102 through the same step thereof is a lower electrode, the pixel electrode 1131 is an upper electrode, and the gate insulating film 1104 and the protective film 1127 interposed between the upper and lower electrodes are a dielectric body.
In order to manufacture the conventional inverted staggered TFT of channel stopper type and the conventional pixel portion including the inverted staggered TFT, first, a first conductive film 1161 is formed over the substrate 1101, and resist masks 1162 are formed over the first conductive film 1161 (see FIG. 8A).
Here, the resist mask is formed through a process including the steps of application of a resist material, exposure of the resist material to light using a photomask, and development of the exposed material. In the case of exposing the applied resist material to light from an upper side, one photomask is needed for forming the resist mask. In other words, a first photomask is needed for forming the resist masks 1162.
With use of the resist masks 1162 as masks, the first conductive film 1161 is etched, so that the gate wiring 1102 and the capacitor wiring 1151 are formed. Next, the resist masks 1162 are removed, and the gate insulating film 1104, a semiconductor layer 1105, and an insulating film 1106 are formed. Then, a resist mask 1109 is formed in a region where the channel protective film 1108 is to be formed (see FIG. 8B). In other words, a second photomask is needed for forming the resist mask 1109.
Next, with use of the resist mask 1109 as a mask, the insulating film 1106 is etched, so that the channel protective film 1108 is formed. After the resist mask 1109 is removed, the semiconductor layer 1111 which has an impurity element imparting one conductivity type and a second conductive film 1112 are formed over the semiconductor layer 1105 and the channel protective film 1108. Resist masks 1125 are formed over the second conductive film 1112 (see FIG. 8C). In other words, a third photomask is used.
With use of the resist masks 1125 as masks, the second conductive film 1112 and the semiconductor layer 1111 are etched. At this time, the channel protective film 1108 and the gate insulating film 1104 function as etching stoppers. Accordingly, the second conductive film 1112 is divided, so that the source wiring 1122 and the drain electrode 1121 are formed. Further, the semiconductor layer 1111 which has an impurity element imparting one conductivity type is also divided, so that the source region 1118 and the drain region 1117 are formed. Furthermore, the semiconductor layer 1105 is also etched, and an end thereof is in alignment with ends of the drain region 1117 and the drain electrode 1121. Next, after the resist masks 1125 are removed, the protective film 1127 is formed over an entire surface, and resist masks 1128 are formed (see FIG. 9A). In other words, a fourth photomask is used.
With use of the resist masks 1128, the protective film 1127 is etched, so that a contact hole 1173 is formed. After the resist masks 1128 are removed, a third conductive film 1129 is formed, and a resist mask 1134 is formed in a region which is over the third conductive film 1129 and where the pixel electrode is to be formed (see FIG. 9B). In other words, a fifth photomask is used.
With use of the resist mask 1134 as a mask, the third conductive film 1129 is etched, so that the pixel electrode 1131 is formed. Then, by removing the resist mask 1134, the pixel portion shown in FIG. 7 is completed.